Albert Barnes Commentary Zechariah 7:3

"[and] to speak unto the priests of the house of Jehovah of hosts, and to the prophets, saying, Should I weep in the fifth month, separating myself, as I have done these so many years?" — Zechariah 7:3 (ASV)

Should I weep in the fifth month, separating myself? — “In the fifth month,” from the seventh to the tenth day, Jerusalem was in flames, set on fire by Nebuchadnezzar. “He burnt the house of the Lord, and the king’s house, and all the houses of Jerusalem and every great man’s house he burnt with fire.”

Jerome: “Now since it is said that the temple is built and we see that no cause of sorrow remains, answer, we pray, are we to do this or to change our sorrow into joy?”

Separating myself — This phrase seems to be added to intensify the fast they had kept. The Nazarite was bound to “separate himself from wine and strong drink” (Numbers 6:3), and so they severed themselves to the Lord and consecrated themselves to Him (Numbers 5:0; see the note at Amos 2:11). They had severed themselves from food, from pleasant things, and from pleasure—perhaps from sin for the day—but not abidingly: they had not given themselves to God.

As I have done these so many years — Literally, “how many.” As if, although they knew it was seventy years, they could not count them.